1. Field of the Invention
The present invention relates to a capacitance detection technology for reading the shape of a subject surface with minute asperity such as a fingerprint as a capacitance variation.
2. Description of the Related Art
Japanese Patent Application Laid-Open Nos. H11-118415, 2000-346608, 2001-56204, and 2001-133213 disclose a technology that covers the surface of a sensor electrode, which is formed on a single-crystal silicon substrate, with a dielectric film, and, with a fingerprint potential serving as the reference potential, identifies a fingertip by utilizing the change in the capacitance formed between the fingertip and sensor electrode in accordance with the asperity of the fingerprint.
However, a conventional capacitance-type fingerprint sensor is formed on a single-crystal silicon substrate. Hence, there has been the problem that the fingerprint sensor splits when pressed strongly by a fingertip. In addition, the fingerprint sensor must be formed with a size that is about the size of the area of a fingertip (approximately 20 mm×20 mm), and therefore, the formation of the fingerprint sensor on a single-crystal silicon substrate generates problems such as high costs. In addition, in the case of a conventional constitution, in which capacitance detection circuits, in which a sensor electrode and transistor are combined, are arranged in the form of a matrix, and the variation in the capacitance formed between the sensor electrode and fingertip is utilized to drive the transistor such that a current flows out to an external circuit, there are restrictions on the size of the transistor disposed in the fingerprint detection unit. Therefore, sufficient current drive performance cannot be obtained and there is the problem that high-precision sensing is not feasible, and so forth.